Tools for shaping objects have long been made with a core of some type to reduce weight and cost. Typical are those which use ceramic beads mixed with an epoxy matrix, or nut shells mixed with an epoxy matrix, or a polyester system which is formed to the desired configuration.
Each of the prior art approaches calls for a core which is still lower in weight. For example, the core weights per cubic foot of the prior art approaches are ceramic bead core--32 lbs; walnut shell core--102 lbs; and foamed polyester systems--55 lbs.
In addition to the desirability of still further reductions in core weight is the manufacturing criterion of ease of construction. Ideally, it should not be necessary to build a mold for casting a core. It would be desirable if a core could be produced independently of and simultaneously with construction of the mold for the finished tool.
Illustrative of prior art approaches is U.S. Pat. No. 2,836,530, which discloses a core with a thermosetting resin as a binder with a filler material such as sand or walnut shells. However, problems of dimensional accuracy may remain.
U.S. Pat. No. 3,861,936 discloses a plastic tooling method and apparatus for producing a master tooling model by extruding a layer of carvable epoxy resin at a uniform thickness upon a pre-constructed base. In addition to problems of dimensional stability, the resulting tool requires machining to produce a near net shape. Also, equipment is required for the metering, mixing, and extruding steps.
U.S. Pat. No. 5,247,861 discloses a method of producing laminated plastic tooling suitable for use in forming board material by techniques such as stretch forming and hydro-forming. The method uses a stacked array of plastic boards which are cut to selected lengths and laid up in a pattern representing the desired tool configuration. A machining step is required to produce the final configuration. Disclosed as typical plastic materials include epoxy, polyurethane, or any other thermosetting or thermoplastic material or mixtures of materials having the requisite characteristics. The board materials may include a filler having a suitable shape. Nevertheless, design challenges represented by still further weight reduction are substantially unmet.
Accordingly, there appears a continuing need for improved methods of manufacturing tools for use in forming large sheets of material, such as in the stretch forming of large metal panels.